Understanding how and when crops cope with and respond to stress during reproductive development may be able to forecast total crop production under abrupt climate change. We studied the effect of complete defoliation under time-specific climate-related conditions on inflorescence sex differentiation in oil palm. A total of 162 pisifera oil palm trees were completely defoliated at the rate of three trees per month between July 2007 and December 2011. Complete defoliation significantly increased male inflorescence induction by 104% when compared with control without defoliation. Acute soil water deficit (SWD) of 16.8 mm between the 30th and 60 th day after complete defoliation (DAD) had an additional positive effect on male inflorescence production. A regression analysis on 18 time-specific, climate-related research and two inflorescence-related variables resulted in high regression coefficients for the time period 30 th to 60 th DAD. This is an indication that oil palm responds to complete defoliation stress after a 30-day delaying period. Total soluble sugars measured at 45 DAD showed a depletion of 55% in the leaves and 21% in inflorescence of defoliated trees compared to control trees without defoliation. Preferential sex differentiation in oil palm towards maleness is an acclimation response to the depletion of total soluble sugar inflected by mechanical and soil water deficit stresses. These results shall permit the simulation of male inflorescence induction and yield forecasting in other geographical locations.

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Abstract. Tambunan VB, Apriyanto A, Ajambang W, Etta CE, Sahari B, Buchori D, Hidayat P. 2020. Molecular identification and population genetic study of Elaeidobius kamerunicus Faust. (Coleoptera: Curculionidae) from Indonesia, Malaysia and Cameroon based on mitochondrial gene. Biodiversitas 21: 3263-3270. Oil palm pollinating weevil Elaeidobius kamerunicus is a very important insect pollinator in oil palm plantation. However, there is still lack of information about molecular identification and population genetic study in this species. The purpose of this study was to explore the effectiveness of oil palm pollinating weevil identification using mitochondrial DNA of COI gene and to assess its genetic variation between different locations and countries. We sequenced the DNA barcode of 36 individuals of this species using the mtDNA Cytochrome Oxidase I (COI) gene to explore their genetic variation, identity and phylogenetic relationship. The COI gene sequences generated from this study were successful in identifying E. kamerunicus. Phylogenetic analysis also revealed 3 well-supported monophyletic haplogroups of E. kamerunicus population. In addition, genetic differentiation analysis revealed that most populations from Indonesia were different from Malaysian and Cameroonian populations indicating that there was a genetic variation between the population samples from these countries. The overall E. kamerunicus used in this study were geographically structured in two regions; outside Indonesia region (Cameroon and Malaysia) and Indonesia region. These results demonstrate the feasibility of using COI gene sequence for molecular identification and population genetic study of E. kamerunicus species.

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